If you want to get specific, Nokia and Microsoft first teamed up in 2005 to help transfer Windows Media Audio files to Nokia phones. But the relationship that led to the recent acquisition started just a few years ago.

August 2009Microsoft, Nokia ink mobile Office dealOne the earliest partnerships between Nokia and Microsoft had nothing to do with Windows Phone. Instead, the two companies got together to build a mobile version of Microsoft Office that could run on Nokia's Symbian phones. Though he would later become Nokia's CEO, Stephen Elop worked at Microsoft at the time and was part of the mobile Office efforts.

September 2010Microsoft exec Elop named Nokia CEOStephen Elop, the head of Microsoft's Business Division, jumped ship from Microsoft to become Nokia's CEO. Elop replaced Olli-Pekka Kallasvuo and was hired to help usher in new changes at Nokia.

February 2011Microsoft and Nokia announce proposed Windows Phone partnershipIn February 2011, Microsoft CEO Steve Ballmer and Nokia CEO Stephen Elop announced that the two companies were teaming up to build Windows Phone devices. The hope was to bolster the Windows mobile ecosystem to a level where it could to compete with Google's Android and Apple's iOS platforms.

February 2011Nokia CEO talks about the Microsoft partnership at Mobile World CongressJust a few days after Microsoft and Nokia announced they were coming together to work on Windows Phone, Nokia's Elop took the stage at Mobile World Congress in Barcelona to make his case about the partnership. He talked about how Nokia would save a significant amount of money to not build a mobile operating system and just focus on hardware.

October 2011Nokia announces its first Windows PhonesAt a press conference in London,Nokia showed off its first Windows Phone devices, the Lumia 800 and Lumia 710. The Lumia 800 was the flagship phone, selling first in the UK and parts of Europe for 420 euros, while the 710 was the first budget Windows Phone device in Nokia's lineup. Both phones shipped with Windows Phone 7.5 Mango and came with Nokia and Microsoft apps preinstalled.

September 2012First flagship Windows Phone 8 device announcedNokia CEO Elop showed off the Lumia 920, the first phone to run the next version Microsoft's mobile operating system, Windows Phone 8. Nokia made a big push for a better camera with the 920 and included wireless charging.

October 2012Windows Phone 8 launchesMicrosoft held a press conference in October 2012 to show off the official release Windows Phone 8. Some of the new features included Kid's Corner, People Hub, and Skype. Though HTC, Samsung, and Nokia phones were used to demonstrate the new features, Microsoft's Ballmer noted that Nokia had sold the most Windows Phones so far.